1. Field of the Invention
This invention relates to an improved original process for synthesising N-isopropyl-N'-o-carbomethoxyphenylsulphamide.
N-isopropyl-N'-o-carbomethoxyphenylsulphamide is known as an intermediate from which an important selective herbicide, namely Bentazon, can be synthesised. This is the reason for the considerable importance of this product and the considerable interest in its production.
2. Description of the Prior Art
It is known from the literature (Kemia-Kemi 9, 1974 page 591) that said intermediate can be prepared by reacting anthranilic acid methyl ester with isopropylsulphamoylchloride, in accordance with the scheme: ##STR1##
The drawback of this method is that it uses isopropylsulphamoylchloride as raw material, this being an intermediate which is very difficult to synthesise.
In this respect, as described in AGEW. CHEM. INT. ED. ENGL. 20, 151-164 (1981), the following synthesis paths are possible: ##STR2## this being a reaction which is difficult to carry out industrially because of the need to use special pressurised equipment; ##STR3## this being a reaction which uses acetonitrile as solvent, and is recommended only for laboratory tests in that the solvent undergoes partial chlorination to 2,4,6-tris(trichloromethyl)-1,3,5 triazine; ##STR4## these being reactions involving the use of phosgene, leading to all the dangers connected therewith.
Moreover, when the sulphamoylchloride has been prepared, it must always be purified by distillation under high vacuum in order to prevent decomposition, this requiring the use of special equipment such as film evaporators which complicates and makes costly its industrial application.